"We believe our cut-points more accurately reflect the changing population trends of older Americans and that muscle weakness is a serious public health concern," said Dr Duchowny.

"Many ageing studies—not just those on muscle strength—are conducted on largely white populations. However, as the U.S. population becomes increasingly diverse, it is critical to use nationally representative data for these types of studies."

Those who fell into the "weak" category were more than 50 per cent more likely to die early than stronger people.

Scott Laidler, celebrity online PT, told The Sun that "it's a great idea to lift weights into your old age" but that caution should be exercised.

"As we get older the intensity of our workouts should decrease and the length of time between them should increase as the recovery gets slower.

"While there are many benefits to lifting weights as an older person, taking on too much too soon or attempting exercise you have not been formally instructed on could be dangerous and heighten your risk of injury.

"Making sure you have an equal focus on your strength, fitness, mobility and aesthetics would be a healthy way to approach exercise and will set you up in very good stead for your future."